The present invention relates to a cylindrical nonaqueous secondary cell which may be used in an electric automotive vehicle or the like to obtain a high energy density and a large capacity.
Recently, electronic equipment has been provided with a high performance, miniaturized and made portable by the development of the electronic technology. Accordingly, there is a strong demand that a secondary cell used in the electronic equipment has a high energy density.
A nickel/cadmium battery, a lead storage battery and the like have been conventionally used as the secondary cells to be used in the electronic equipment. However, these batteries are inferior in discharge potential level and it is insufficient to obtain the cells having a high energy density.
Accordingly, a lithium ion secondary cell has been vigorously researched and developed which is of a nonaqueous solution secondary cell using, as a cathode, a lithium ion such as lithium, lithium alloy or carbon material which may be doped or dedoped and using, as an anode, a lithium complex oxide such as a lithium cobalt complex oxide.
The lithium ion secondary cell ha a high battery voltage and a high energy density and is superior in self-discharge property and recycle characteristics. In particular, there is a strong demand in developing a battery having a high voltage (several tens to several hundreds of volts), a high energy capacity and a high energy density for use in a power storage station or an electric vehicle for the purpose of saving energy and moderating the contamination of the environment.
A cylindrical, nonaqueous electrolytic solution secondary battery in which a spiral electrode laminate structure formed by winding strip-shaped cathodes and anodes through separators is received in a cylindrical metal case has been proposed as a structure of the lithium ion secondary cell. It is possible to increase an electrode area by forming the nonaqueous electrolytic solution secondary cell into the spiral electrode laminate structure and to obtain a cell which is superior in load characteristics.
On the other hand, such a nonaqueous electrolytic solution secondary cell having the spiral electrode laminate structure with a high voltage and a high capacity suffers from a problem that the heat is generated upon the discharge.
Also, in the cylindrical nonaqueous electrolytic solution secondary cell, it is necessary to seal both ends of the cylindrical metal case with sealing plates. In general, it is proposed to use an argon welding to attach the sealing plates to both ends of the metal case. However, there is a fear that the heat generated during the argon welding would damage the spiral electrode laminate structure.
In this case, if a laser welding is used instead of the argon welding, the heat problem would be moderated to some extent. However, when the laser welding is carried out, it is difficult to obtain a reliability of the sealing of the interior of the cell with the sealing plates. Also, in order to enhance the sealability, it takes a long period of time for welding operation, which leads to the degradation of the productability. Although it is possible to theoretically apply a microwave welding to this, it is actually impossible to use this technology because of the reliability of the sealing is low.
Also, the cell case of the conventional cylindrical nonaqueous electrolytic solution secondary cell has been made of steel or nickel-plated stainless steel in view of the durability and the mechanical strength. However, since these materials have a large specific weight and are heavy, these materials are disadvantageous in weight energy density. Accordingly, it has been proposed to use a case made of light metal such as aluminum or titanium (in this case, connected to the anode) to thereby reduce the weight.
However, titanium is expensive as a constituent material for the nonaqueous electrolytic solution secondary cell. Accordingly, it would be difficult to use a large amount of titanium in a general field. It is practically general to use aluminum for the cell case in view of the durability.
However, the aluminum is lower in mechanical strength than the steel or the like. In the case where the cell case is made of material has a thickness which may sufficiently attain the object, it is impossible to obtain a necessary compression of a plastic-made gasket due to the insufficient mechanical strength with a sealing portion structure obtained by press-fitting the gasket between the metal portions and sealing the opening portion of the cell case by the stress.
Also, inversely, in the case where the cell case is made of a material having a thickness that may ensure the sufficient compression of the gasket with such a sealing portion, the purpose of sufficiently reducing the weight could not be attained.